The light weight metals of aluminum and magnesium have very large markets for they are utilized in a wide variety of industries. In a lesser way, titanium is also utilized as a light weight fabrication material. These metals suffer from some drawbacks, however, which limit their usefulness. These include low stiffness (low modulus of elasticity), high thermal coefficient of expansion, and low strength. Some of these drawbacks have been overcome through the use of metal matrix composites of these metals. Typically, ceramics are added to the metals. The primary objectives of these additives have been to increase the modulus of elasticity and to reduce the thermal coefficient of expansion. When fibrous material, such as silicon carbide whiskers, are added, strengthening has been observed. Other added materials include the fibers of boron metal, carbon, aluminum silicate, and aluminum oxide. Still other typical strengthening agents are aluminum oxide particulates, boron carbide and silicon carbide in various forms.
Of these, only aluminum oxide particulate and silicon carbide particulate have been extensively utilized in the aluminum-based matrix. To add either of these to molten aluminum, a continuous stirring action must be utilized because the specific gravities of the additives are significantly greater than the molten aluminum. Similar problems would be observed with molten magnesium. The continuous stirring causes oxide inclusions and hydrogen to contaminate the melts. Furthermore, because of the contamination and the non-uniform nature of the metal matrix composites (MMC'S), remelting (for recycle, etc.) is a problem due to the variability of the resulting feed product.
Accordingly, it is an object of the present invention to provide a metal matrix composite using aluminum, magnesium and titanium wherein a minimum of stirring is required to maintain the additive material in suspension.
It is another object of the present invention to provide a metal matrix composite wherein the strengthening agent has a specific gravity very like that of the molten metal whereby there is little settling of the strengthening agent during the formation of the metal matrix composite.
A further object of the present invention is to provide a metal matrix composite of aluminum, magnesium or titanium that can be more easily machined.
Also, it is an object of the present invention to provide a metal matrix composite of aluminum or magnesium that can be easily remelted to better utilize unused portions.
These and other objects of the present invention will become apparent upon a consideration of the following detailed description.